U.S. patent application number 13/028475 was filed with the patent office on 2011-08-18 for method and system for optical connection validation.
This patent application is currently assigned to CIENA CORPORATION. Invention is credited to Choudhury AL SAYEED, David BOERTJES, Marc DESJARDINS.
Application Number | 20110200324 13/028475 |
Document ID | / |
Family ID | 44369718 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110200324 |
Kind Code |
A1 |
BOERTJES; David ; et
al. |
August 18, 2011 |
METHOD AND SYSTEM FOR OPTICAL CONNECTION VALIDATION
Abstract
An optical add/drop multiplexer (OADM) having an Add path for
adding optical channel signals input through a plurality of Add
ports to an outbound dense wavelength division multiplexed (DWDM)
signal, and a Drop path for switching selected channels from an
inbound DWDM signal to one or more of a plurality of Drop ports.
The OADM has a loopback connection between the Add path and the
Drop path. The loopback connection couples a selected loopback
channel wavelength from the Add path to the Drop path. The physical
connection between a transceiver and the OADM can be verified by
connecting the transmitter to an Add port of the OADM and the
receiver to a Drop port of the OADM. The OADM is controlled to
switch the selected loopback channel wavelength in the Drop path to
at least one intended drop port to which the receiver should be
connected, and the transmitter is controlled to transmit a
predetermined test signal using the loopback channel wavelength.
Detecting the test signal by the receiver verifies that the
receiver is connected to the at least one intended drop port.
Inventors: |
BOERTJES; David; (Nepean,
CA) ; DESJARDINS; Marc; (Ottawa, CA) ; AL
SAYEED; Choudhury; (Ottawa, CA) |
Assignee: |
CIENA CORPORATION
Linthicum
MD
|
Family ID: |
44369718 |
Appl. No.: |
13/028475 |
Filed: |
February 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61305026 |
Feb 16, 2010 |
|
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|
Current U.S.
Class: |
398/16 ;
398/48 |
Current CPC
Class: |
H04J 14/0209 20130101;
H04J 14/0212 20130101 |
Class at
Publication: |
398/16 ;
398/48 |
International
Class: |
H04B 10/08 20060101
H04B010/08; H04J 14/02 20060101 H04J014/02 |
Claims
1. A method of connecting a transceiver including a transmitter and
a receiver to an optical add/drop multiplexer (OADM), the method
comprising: providing a loopback connection between an Add path and
a Drop path of the OADM, the loopback connection coupling a
selected loopback channel wavelength from the Add path to the Drop
path; connecting the transmitter to an Add port of the OADM;
connecting the receiver to a Drop port of the OADM; controlling the
OADM to switch the selected loopback channel wavelength in the Drop
path to at least one intended drop port to which the receiver
should be connected; controlling the transmitter to transmit a
predetermined test signal using the loopback channel wavelength;
and detecting the test signal by the receiver to verify that the
receiver is connected to the at least one intended drop port.
2. The method of claim 1, wherein the selected loopback channel
wavelength lies outside a transmission band of a dense wavelength
division multiplexed (DWDM) signal.
3. The method of claim 2, wherein the step of providing a loopback
connection comprises providing a pair of fixed wavelength filters
disposed in a loopback path between the Add path and the Drop path
of the OADM, the fixed wavelength filters being configured to pass
the selected loopback channel wavelength and reflect other
wavelengths.
4. The method of claim 2, wherein the step of providing a loopback
connection comprises providing a tuneable filter disposed in a
loopback path between the Add path and the Drop path of the OADM,
the tuneable filter being tunable to pass the selected loopback
channel wavelength.
5. The method of claim 1, wherein the selected loopback channel
wavelength corresponds with a channel of a dense wavelength
division multiplexed (DWDM) signal.
6. The method of claim 5, wherein the step of providing a loopback
connection comprises: providing a jumper between a predetermined
output port and a corresponding input port of a wavelength
selective switch coupled to the OADM; and controlling the
wavelength selective switch to switch the selected loopback channel
wavelength to the predetermined output port, such that the jumper
will couple the test signal to the corresponding input port of the
wavelength selective switch.
7. The method of claim 5, wherein the step of providing a loopback
connection comprises: providing a jumper between respective common
ports of an Add path wavelength selective switch and a Drop path
wavelength selective switch; and controlling the Add path
wavelength selective switch to switch the selected loopback channel
wavelength to its respective common port such that the jumper will
couple the test signal to the corresponding common port of the Drop
path wavelength selective switch.
8. An optical add/drop multiplexer (OADM) having an Add path for
adding optical channel signals input through a plurality of Add
ports to an outbound dense wavelength division multiplexed (DWDM)
signal, and a Drop path for switching selected channels from an
inbound DWDM signal to one or more of a plurality of Drop ports,
the OADM comprising: a loopback connection between the Add path and
the Drop path of the OADM, the loopback connection coupling a
selected loopback channel wavelength from the Add path to the Drop
path.
9. The OADM of claim 8, wherein the selected loopback channel
wavelength lies outside a DWDM transmission band.
10. The OADM of claim 9, wherein the loopback connection comprises
a pair of fixed wavelength filters disposed in a loopback path
between the Add path and the Drop path, the fixed wavelength
filters being configured to pass the selected loopback channel
wavelength and reflect other wavelengths.
11. The OADM of claim 9, wherein the loopback connection comprises
a tuneable filter disposed in a loopback path between the Add path
and the Drop path, the tuneable filter being tunable to pass the
selected loopback channel wavelength.
12. The OADM of claim 8, wherein the selected loopback channel
wavelength corresponds with a channel of the DWDM transmission
band.
13. The OADM of claim 12, wherein the loopback connection
comprises: a jumper between a predetermined output port and a
corresponding input port of a wavelength selective switch coupled
to the OADM; wherein the wavelength selective switch is controlled
to switch the selected loopback channel wavelength to the
predetermined output port, such that the jumper will couple the
test signal to the corresponding input port of the wavelength
selective switch.
14. The OADM of claim 12, wherein the loopback connection
comprises: a jumper between respective common ports of an Add path
wavelength selective switch and a Drop path wavelength selective
switch; wherein the Add path wavelength selective switch is
controlled to switch the selected loopback channel wavelength to
its respective common port such that the jumper will couple the
test signal to the corresponding common port of the Drop path
wavelength selective switch.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present invention is based on, and claims benefit of
provisional U.S. patent Application No. 61/305,026 filed Feb. 16,
2010, the entire content of which is hereby incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates generally to fibre-optic
communication systems, and in particular to techniques for
validating optical connections in a fibre-optic communication
system.
BACKGROUND
[0003] Fibre optic networks often employ tuneable technologies both
for optical add/drop ports and for transmitters. Transmitters using
tuneable lasers are desirable for several reasons. First, tuneable
lasers reduce the number of product variants required to construct
the network. For example, a Dense Wavelength Division Multiplexed
(DWDM) communications band typically has 80 channels. If fixed
wavelength (i.e. non-tuneable) lasers are used to drive this
channel band, then 80 different variants of the transmitter laser
are required. This is problematic, especially for customers who
must maintain an inventory of appropriate transmitter components
for replacement in the case of failure (sometimes called
"sparing"). The second reason is that the use of tuneable lasers
enables re-tuning the transmission wavelength of any given channel
in the system for the purpose of reconfiguration, which in turn
enables the implementation of an Optical Add/Drop Multiplexer
(OADM).
[0004] The Add portion of an OADM can be made tuneable by including
a tuneable filter which is tuned in conjunction with the
transmitter laser. Prior to the introduction of practical Digital
Signal Processor (DSP) based coherent transmitters, it was
commonplace to use Distributed Feedback (DFB) or Distributed Bragg
Reflector (DBR) tuneable laser designs, which have significant out
of band noise in the form of side modes and spontaneous emission.
This noise needed to be rejected, which drove the need for
filtering the laser output light.
[0005] Prior to the introduction of practical DSP based coherent
receivers, it was commonplace to use direct detection receivers. In
a DWDM system, direct detection receivers require optical filters
to separate a desired one wavelength channel from the DWDM signal,
and present the separated channel light to the receiver for
detection. This type of receiver can detect any wavelength which
the optical filter chooses. Therefore, the drop portion of the OADM
can be made tuneable by including a tuneable filter.
[0006] However, tuneable filters are expensive. Reducing the number
of tuneable filters is advantageous. With coherent
transmitters/receivers, it is possible to reduce or eliminate the
filtering from the adds/drops. For example, please refer to
PCT/CA2009/001455 titled COHERENT AUGMENTED OPTICAL ADD-DROP
MULTIPLEXER and filed on Sep. 11, 2009 which is herein incorporated
by reference in its entirety. The result is to replace the optical
filters with couplers and splitters which are not wavelength
selective.
[0007] In a typical OADM, transmitters/receivers and the Add/Drop
multiplexer are constructed as separate components, and connected
together by manually installed fibre cables. This arrangement
allows the user to upgrade a system by adding individual channels
over time. However, the manual installation of fibre cables leads
to a risk of misconnections due to human error.
[0008] The challenge in this case is that in the absence of
filtering in the Add/Drop multiplexer, misconnections can be made
which place two transmitters of the same wavelength on the same
Add/Drop multiplexer. This situation will result in an outage on
the affected channel(s).
[0009] It is, therefore, desirable to provide a technique for
preventing the connection of a transmitter to an optical
communications system of a transmitter which is tuned to a channel
already in use.
SUMMARY
[0010] Aspects of the present invention provide methods and systems
to validate the physical connection between the
transmitter/receiver and the add/drop multiplexer so as to
eliminate traffic outages caused by fibre misconnections. Through
the knowledge of where a transmitter/receiver is connected, the
system can prevent the tuning of the laser to a wavelength which
already exists in the OADM, thereby eliminating the possibility of
a traffic outage by such a fibre misconnection.
[0011] According to one aspect, a loop back is added which allows
for the testing of each newly added transmitter. The loopback
allows for the local testing of the placement of the newly added
transmitter. Once the placement is confirmed, the channels already
in use for that placement are either known, or can be confirmed
through testing. For example, each newly added transmitter is
initially tuned to some channel that is not to be used by the
system (for example a channel just outside the range of the DWDM
transmission band), and the loopback allows for the local testing
of the placement of the newly added transmitter on such an un-used
channel. Finally, the system is trained to use this out-of-band
channel to determine which add/drop that any new transmitter and
receiver is connected to. Then the in-use channels are removed from
the list of available channels that this transmitter may use.
Accordingly, the newly added transmitter can be tuned to a channel
which is not in use.
[0012] Optionally, power monitoring taps are added to the inputs to
determine which of the add/drop ports are connected to a
transponder. This is particularly useful for modules which use
power combiners and splitters, which make it otherwise difficult to
determine which port or port pair is used, as the ports are
difficult to differentiate after combining/spitting.
[0013] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Representative embodiments of the invention will now be
described by way of example only with reference to the accompanying
drawings, in which:
[0015] FIG. 1 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer of a type in which
techniques in accordance with the present invention may be
implemented;
[0016] FIG. 2 is a block diagram schematically illustrating a
network node incorporating a coherent augmented add/drop
multiplexer;
[0017] FIG. 3 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
representative embodiment of the invention.
[0018] FIGS. 4a and 4b are perspective views showing a paired or
duplex connectors usable in the coherent augmented add/drop
multiplexers of FIGS. 1 and 3;
[0019] FIG. 5 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
further representative embodiment of the invention;
[0020] FIG. 6 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
further representative embodiment of the invention;
[0021] FIG. 7 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
further representative embodiment of the invention;
[0022] FIG. 8 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
further representative embodiment of the invention; and
[0023] FIG. 9 is a block diagram schematically illustrating a
coherent augmented add/drop multiplexer in accordance with a
further representative embodiment of the invention
[0024] It will be noted that throughout the appended drawings, like
features are identified by like reference numerals.
DETAILED DESCRIPTION
[0025] Generally, the present invention provides a method and
system for connection testing and/or validation of a newly added
transmitter.
[0026] FIG. 1 is a block diagram schematically illustrating
principal elements of a reconfigurable optical add/drop multiplexer
(ROADM) 2 in which coherent transmitter (Tx) and Receiver (Rx)
technology is used to eliminate some of the filtering which is
normally required. The add/drop 2 may be connected to send and
receive optical dense wavelength division multiplexed (DWDM)
signals. In FIG. 1, this connection is represented by an optical
fiber span pair 4 connected to respective broadband optical ports 6
of the add/drop 2. However, it will be appreciated that, in many
applications, optical routing and switching devices will be
connected between the add/drop 2 and the fiber span pair 4, as will
be described in greater detail below.
[0027] As may be seen in FIG. 1, the ROADM 2 is provided as a set
of modules 8-12 interconnected by optical fiber intra-node
connections 14-16. In the embodiment of FIG. 1, the modules forming
the ROADM 2 comprise an amplifier module 8, a second-stage
MUX/DeMUX module 10; and one or more first-stage MUX/DeMUX modules
12. The interconnections 14, 16 between these modules define a Drop
path and a Add path of the ROADM 2.
[0028] The Drop path comprises a receive amplifier 18 in the
amplifier module 8 for amplifying an inbound dense wavelength
division multiplexed (DWDM) light (received through the input
Broadband port 6a; a wavelength selective switch (WSS) 20 in the
second-stage MUX/DeMUX module 10 for routing any selection of
channels of the received DWDM light to any of a set of output
fibers; and a power divider 22 of the first-stage MUX/DeMUX module
12 for receiving a respective one of the selections of channels,
and supplying the light of these channels to a plurality of
coherent receivers 24 (only one shown in FIG. 1). With this
arrangement, each coherent receiver 24 receives a portion of the
light from all of the selected channels on it's respective
first-stage MUX/DeMUX module 12, representing only a portion of the
received DWDM light, which has a benefit of reducing the common
mode rejection performance requirement of the coherent receiver 24
as compared to the requirement when receiving light from all of the
channels in the DWDM signal.
[0029] The Add path generally mirrors the Drop path, by combining
individual channel signals from a plurality of transmitters 26 into
an outbound dense wavelength division multiplexed (DWDM) light that
is output though the output broadband port 6b. In the embodiment of
FIG. 1, the Add path comprises a respective power combiner 28, 30
in each of the first- and second-stage MUX/DeMUX modules 12, 10,
and a launch amplifier 32 in the amplifier module 8. The
first-stage power combiner 28 operates to combine light from a
plurality of transmitters 26 (only one is shown in FIG. 1) onto a
single fiber that is connected to the second-stage MUX/DeMUX module
10. When each of the transmitters 26 is tuned to emit light
corresponding to a respective different narrow band wavelength
channel, the light passed to the second-stage MUX/DeMUX module 10
will be a wavelength division multiplexed (WDM) light comprising
each of the transmitted wavelength channels. The second-stage power
combiner 30 operates to combine a plurality of channels' light
(from respective first-stage power combiners 28) for transmission
through the output broadband port 6b. The Add path amplifier 32 is
coupled to output broadband port 6b, and operates to amplify the
DWDM signal for transmission through downstream optical components,
such as the optical fiber span 4.
[0030] The block diagram of FIG. 1 only shows a single first-stage
MUX/DeMUX module 12 connected to the second-stage MUX/DeMUX module
10. However, it will be appreciated that there can be any number of
first-stage MUX/DeMUX modules 12, up to the maximum number of
inputs supported by the second-stage MUX/DeMUX module 10.
[0031] FIG. 2 is a block diagram illustrating a representative
network node comprising a directionally independent access (DIA)
card 34 optically coupled to three fiber spans 4a-c via respective
Optical Transmission Sections (OTSs) 36a-c. As may be seen in FIG.
2, the DIA 34 comprises the ROADM 2 of FIG. 1 coupled to a
wavelength selective switch (WSS) 38 which is programmed to
selectively switch channels between the ROADM 2 and each of the
three OTSs 36. This arrangement combines Rx/Tx tunability with
optical switching to enable the DIA 34 to add/drop channels to/from
DWDM signals in any of three fiber spans 4a-c. The system shown in
FIG. 2 has only one DIA 34 connected to three OTSs 36, whereas a
typical network node may have more than one DIA 34, each of which
is connected to two or more OTSs 36.
[0032] The arrangement of FIGS. 1 and 2 have an advantage in that
the MUX/DeMUX operations are performed with very limited optical
filtering. However, this advantage is fully realized when the
transmitters 26 are tuneable within the entire spectral range of
DWDM transmission. This degree of Tx tunability creates a risk of
misconnection, in which two or more transmitters 26 connected to
the Add ports of a given first-stage MUX/DeMUX module 12, are tuned
to the same wavelength. This will cause interference of the
affected optical channel signals because there is no filtering
between the Add ports, and the associated WSS 38 cannot switch the
(interfering) channel signals in the DWDM signal received from the
ROADM 2 to different OTSs 36. Consequently, the interfering channel
signals will be transmitted through the network, and produce a loss
of signal condition at the receiver (referred to as an `outage`)
affecting both channel signals.
[0033] FIG. 3 is a block diagram illustrating a ROADM 40 in
accordance with a first representative embodiment of the present
invention. As may be seen in FIG. 3, the ROADM 40 is closely
similar to that of FIG. 1, and can therefore be used in the DIA 34
of FIG. 2. However, the ROADM 40 of FIG. 3 differs from that of
FIG. 1, in that it incorporates a loop-back connection 42 which is
designed to couple a selected loop-back channel directly from the
Add path to the Drop path. In some embodiments, the loop-back
connection 42 may comprise a pair of inexpensive fixed frequency
optical filters 44a-b designed to pass the selected loop-back
channel wavelength, while reflecting out-of band signals. In some
embodiments the loop-back channel wavelength is chosen so that it
does not correspond with a channel that is normally used in the
system. For example, the loop-back channel wavelength may lie
outside the DWDM transmission band. With this arrangement, the
out-of-band wavelengths rejected by the filters 44 will correspond
with the DWDM transmission band, so that isolation between the Add
and Drop paths is maintained for DWDM transmission band.
[0034] The loop-back connection 42 can be used to determine the
add/drop ports that a new transmitter/receiver pair is connected
to. This is achieved by programming the WSS 20 of the second-stage
MUX/DeMUX module 10 to switch the loop-back channel to the specific
first-stage divider 22 to which the new receiver 24' should be
connected. The new transmitter 26' can then be tuned to the
loop-back channel wavelength, and driven to transmit a
predetermined test signal (such as, for example, a signal contain
identification information of the new transmitter). As may be seen
in FIG. 3, this test signal (in the loop-back-channel) will be
routed through the loop-back connection 42 to the second-stage WSS
20 and switched to the intended first-stage divider 22. If the new
receiver 24' is in fact connected to a Drop port of the intended
divider 22, it will receive the test signal, which enables
verification that the new receiver 24' and transmitter 26' have
been properly connected to the ROADM 40. Then, the channel
wavelengths already in use (by other transmitters, not shown,
connected to the ROADM 40) can be removed from the set of channel
wavelengths that the new transmitter 26' may use. In this way,
connection between the ROADM 40 and the new receiver 24' can be
verified, and the new transmitter 26' can be prevented from tuning
to channel wavelength which already is carrying traffic (and
thereby and causing an outage).
[0035] Loopback can be active for one or more channels depending on
the characteristics of the filter 44 used in the loop-back
connection 42 and the number of channels which can be switched by
the WSS 20. Loopback may be active for more than just the time it
takes to do the connection validation. It may be useful for idle
transponders (those which are not yet carrying traffic, or which
have been taken out of active service) to have a loopback active to
monitor their performance, so that when it is decided to put them
into service for carrying traffic, one has a greater confidence
that they are working properly.
[0036] As is known in the art, optical components and connections
are typically packaged as paired units. For example, a receiver and
a transmitter will normally be packaged together as a transceiver,
which may have a form illustrated in FIG. 4a. Similar paired
packaging is commonly used for MUX/DeMUX modules, Add and Drop
ports, and fiber transmission cables. Accordingly, the risk of
misconnection in fibre optic systems can be reduced by providing
duplex, or paired optical connectors, with duplex fibres and duplex
receptacles, such as may be seen in FIG. 4b. In this way, one can
be sure that the transmitter and receiver packaged together in a
given transponder are connected to the same port pair of the first
MUX/DeMUX module 12, and then verification of whether or not it is
the correct port pair can be performed using the methods described
above with reference to FIG. 3.
[0037] As may be appreciated, a colourless ROADM provides many
opportunities for making paired connections. For example, paired
connections can be used for either (or both) of the intra-nodal
connections 14-16 of the ROADMs of FIGS. 1-3. Paired connections,
in conjunction with the loopback verification technique described
above, validates both the transmitter and receiver connections, as
well as those between the first and second-stage MUX/DeMUX modules
10-12.
[0038] FIG. 5 shows another embodiment in which, instead of having
a fixed wavelength loop-back channel, any channel that is
switchable by the WSS 20 can be used for connection validation. In
this case, the loopback connection 46 comprises an optical tap 48
which takes some of the light from the Add path, and redirects it
to a tunable filter (TF) 50. This TF 50 can be tuned to a desired
channel wavelength that is being used for connection validation,
which could be any channel in the DWDM transmission band, or an
out-of-band channel if desired. A second tap 52 can then be used to
insert the loopback channel into the Drop path. An amplifier 54 may
be provided, if desired, in order to overcome losses through the
loopback connection 46. When the loopback connection 46 is not
active, the tunable filter 50 may be tuned to an unused part of the
DWDM transmission spectrum, and/or the amplifier 54 may be turned
off.
[0039] FIGS. 6a-b show another embodiment for achieving optical
connection validation. The previously discussed embodiments utilize
a loopback connection 42,46 that is incorporated within the ROADM
40 and so does not rely on external components (such as the WSS 38
of a DIA card 34 to for connection validation. In fact, the
embodiments of FIGS. 3 and 5 can operate in an OADM or
point-to-point architecture in addition to a DIA. The embodiment of
FIG. 6, on the other hand, is tailored to the DIA architecture, but
has the advantage of not requiring any filters in the loopback
connection. As may be seen in FIG. 6a, a loopback connection 56
uses a fibre jumper 58 connecting a pair of ports of the WSS 38.
The WSS 38 can be programmed to send one or more channels through
this loopback connection 56, by directing the desired channel(s) to
the associated output port (in FIG. 6a, the loopback connection 56
is provided on the Output/Input port labelled "switch 9" but any
other port pair may be used). With this arrangement, connection
verification using the methods described above can be accomplished
for any one or more channels simultaneously, limited only by the
wavelength switching capability of the WSS 38.
[0040] FIG. 6b illustrates a variation of this approach, in which
the loopback connection 56 further includes a power divider 60 and
(optionally) an amplifier 62. In some cases, the power divider 60
and amplifier 62 may be incorporated in the WSS 38. In other cases,
the power divider 60 and amplifier 62 may be integrating into a
package with the jumper 58. The arrangement of FIG. 6b is
beneficial in that enables test signals generated during loop-back
operation to be tapped from the loopback connection 56 and used,
for example, for evaluating performance of the DIA 34 in addition
to connection verification.
[0041] FIG. 7 illustrates the method of FIGS. 6a-b applied to an
Add/drop multiplexer that utilizes a fixed wavelength filter-based
MUX/DeMUX module 64. In this case, the risks associated with
misconnecting transmitters/receivers to the Add/Drop ports of the
MUX/DeMUX module 64 are reduced, but the loopback connection 56 is
still useful for validating the intra-nodal connections 66-68
between the modules, a well as stand-by capacity monitoring.
[0042] As noted above with reference to FIGS. 3 and 4, the loopback
process can be used to validate that a new receiver 24' is
connected to the correct first-stage power divider 22. When paired
components and duplex connections are used (as described with
reference to FIG. 4), this approach helps to ensure that a
transceiver (transmitter/receiver pair) are connected to the
correct MUX/DeMUX module 12 (comprising a matched pair of divider
22/combiner 28 for the Drop and Add paths, respectively). However,
it does not provide any indication of the specific Add/Drop port of
the MUX/DeMUX module 12 to which the transceiver is connected. FIG.
8 illustrates an embodiment in which the Add path input ports, in
both the first and second MUX/DeMUX modules 10 and 12 are provided
with power taps 70, which enable the signal received through each
port to be monitored. With this arrangement, when the connection of
a new transponder is being verified, a monitoring subsystem (not
shown) can examine each of the input ports to detect the presence
of the test signal being transmitted by the new transmitter 26, and
so determine which port the transponder is connected to. This
connection validation can be performed equally for transponders
connected to the first-stage MUX/DeMUX module 12 or to the
second-stage MUX/DeMUX module 10, as may be seen in FIG. 8.
[0043] FIG. 9 illustrates an embodiment in which the second level
MUX/DeMUX module 10 comprises a respective 2.times.8 wavelength
selective switch 72, 74 in each of the Add and Drop paths. In this
case, each of these WSSs 72, 74 is configured with two common
ports, one of which is connected to facilitate Add/Drop signal path
operation. The second common port of each WSSs 72, 74 are used for
the loop-back connection. As may be seen in FIG. 9, a loopback
connection 76 uses a fibre jumper 78 connecting the second common
ports of the WSSs 72, 74. The Add-path WSS 72 can be programmed to
send one or more channels through this loopback connection 76, by
directing the desired channel(s) to the associated common port.
With this arrangement, connection verification using the methods
described above can be accomplished for any one or more channels
simultaneously, limited only by the wavelength switching capability
of the WSSs 72, 74. A further advantage of this arrangement is that
filters (either fixed or tunable) are not required in the loopback
connection 76.
[0044] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments of the invention. However, it will
be apparent to one skilled in the art that these specific details
are not required in order to practice the invention. In other
instances, well-known electrical structures and circuits are shown
in block diagram form in order not to obscure the invention. For
example, specific details are not provided as to whether the
embodiments of the invention described herein are implemented as a
software routine, hardware circuit, firmware, or a combination
thereof.
[0045] Embodiments of the invention can be represented as a
software product stored in a machine-readable medium (also referred
to as a computer-readable medium, a processor-readable medium, or a
computer usable medium having a computer-readable program code
embodied therein). The machine-readable medium can be any suitable
tangible medium, including magnetic, optical, or electrical storage
medium including a diskette, compact disk read only memory
(CD-ROM), memory device (volatile or non-volatile), or similar
storage mechanism. The machine-readable medium can contain various
sets of instructions, code sequences, configuration information, or
other data, which, when executed, cause a processor to perform
steps in a method according to an embodiment of the invention.
Those of ordinary skill in the art will appreciate that other
instructions and operations necessary to implement the described
invention can also be stored on the machine-readable medium.
Software running from the machine-readable medium can interface
with circuitry to perform the described tasks.
[0046] The above-described embodiments of the invention are
intended to be examples only. Alterations, modifications and
variations can be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
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